The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, a brake system used for a vehicle is classified into a foot brake system in which a driver presses his or her foot down on a pedal to provide braking force to a vehicle while driving the vehicle, and a parking brake system in which the driver manipulates a lever, or the like at the time of parking or stopping the vehicle to brake the vehicle so that the vehicle is not moved due to external impact or a self load on a slope road, depending on a function of the brake system.
The brake system used for the vehicle may be classified into a disk brake system and a drum brake system, depending on an operation method of the brake system.
Among these, the disk brake system has a structure in which pads provided on both sides of a disk rotated together with a wheel brake the disk by compressing the disk, and is mainly mounted in the front wheels of the vehicle, and the drum brake system has a structure in which a pair of brake shoes provided in a drum rotated together with the wheel are expanded to brake the drum, and is mainly mounted in the rear wheels.
Here, the drum brake system mounted in the rear wheels serves as the parking brake as well as a main brake.
More specifically, the drum brake system is connected to a parking brake lever provided in an interior of the vehicle by a cable. Thus, when a user manipulates the parking brake lever, the brake shoes pulled by the cable are closely adhered to the brake drum, thereby generating the braking force.
Recently, not the drum brake, but the disk brake has also been used for the rear wheels of the vehicle. As such, in the case in which the disk brake is used for the rear wheels, the parking brake is provided independent of the disk brake, which is implemented as a drum in hat (DIH) brake system. The drum in hat brake system has the drum brake system provided in the disk brake system, and the general drum in hat brake system according to the related art is specifically disclosed in the prior art.
An inner diameter part of a hat part provided in a main braking part of the drum in hat brake system as described in the related prior art, which is a portion from which mechanical friction with a friction material is generated, should easily discharge frictional heat and have superior durability. Conventionally, the above-mentioned hat part has mainly used gray cast iron having good heat resistance and wear resistance.
However, the gray cast iron, which is cast iron obtained by educing flake graphite, has good mechanical strength and good corrosion resistance and vibration absorptivity, and the like, while specific gravity thereof is 7.2 g/cm3, which is quite heavy. Thus, the gray cast iron may degrade riding quality, manipulability, and fuel efficiency of the vehicle.
In addition, due to recent issues of exhaustion of oil energy, climate change, and the like, the technology development for improving fuel efficiency is increasing in the global vehicle industry.